Superregenerative receiver



Jan. 2, 1951 K. H. EMERSON SUPERREGENERATIVE RECEIVER 2 Sheets-Sheet 1Filed March 2, 1946 IN V EN TOR. KENNETH H. ME/HON wbr Jan. 2, 1951 K.H. EMERSON SUPERREGENERATIVE RECEIVER 2 Sheets-Sheet 2 Filed March 2,1946 INVENTOR. KENNETH H. EME/HON mitting and receiving equipment.

Patented Jan. 2, 1951 NT OFFICE SUPERREGENERATIVE RECEIVER Kenneth El.Emerson, Philadelphia, Pa., assignor, by niesne assignments, to PhilcoCorporation, Philadelphia, Pa., a corporation of PennsylvaniaApplication March 2, 1946, Serial No. 651,649

This invention relates to improved electrical apparatus forautomatically controlling the regeneration of superregenerative radi-oreceiver circuits. Although the invention is applicable tosuperregenerative receivers generally,

I have found it to be particularly useful in superregenerative receiversemployed in radio ranging systems, for effecting the maximum possiblediscrimination between desired signals and undesired noise. Accordingly,I shall find it convenient n to describe the invention with reference toa par ticular class of radio ranging systems, connection with which mynovel circuit arrangement was conceived, while in no way limiting theinvention to such application. In the copending application or" WilliamE. f Bradley, Serial No. 651,398, filed March l, 1946, is described aradio ranging system in which a superregenerative receiver is unquenchedduring time-spaced intervals, the spacing of which is varied in apredetermined manner so as to render the receiver responsive to receivedsignals produced by reection of transmitted pulses from target objectsat diiierent ranges from the trans- In such sys tems it is desirable tocontrol the regeneration and thereby the sensitivity of thesuperregenerative receiver so as to secure the maximum possiblediscrimination between desired signalsand vundesired noise. This may beeffected by developing in response to the output from thesuperregenerator a control signal which is used to control thesensitivity of the superregenerator. However, if,v as. indicated above,the superregenerator is unquenched only during time-spaced intervals,

and if each unquenching coincides with the ar- 'rival of a receivedpulse signal; the sensitivity control signal developed will depend uponthe magnitude of the received signal, so that there will be a tendencyundesirably to reduce the sensitivity of the superregenerator. Toobviate this diiculty, the superregenerator may be unquenched not onlyduring intervals corresponding to the arrival of desired receivedsignals, but also during other intervals between the arrivals of suchdesired signals. In this manner the sensitivity controlling signaldeveloped in response to the output of the superregenerator is made todepend not only upon the output in the presence of desired receivedsignals, but also upon the out- By making the number of unthe resultantcontrol signal can be made princif pally dependent upon the output ofthe superregenerator produced in response to noise alone.

This permits the superregenerator to be controlled to an optimum levelof sensitivity for maximum discrimination between desired signals andnoise.

The principal object of the invention is to provide a novel and improvedcircuit arrangement for utilizing the control signal thus developed forcontrolling the regeneration and hence the sensitivity of thesuperregenerative amplier.

Essentially the circuit arrangement according to the invention comprisesa control tube having at least triode elements, whose plate and cathodeare respectively connected to the plate and cathode of thesuperregenerative oscillator tube. The plates of the control tube and ofthe oscillator are both supplied with positive potential through acommon impedance which S at least partially resistive. Means are thenprovided for cleriving a control signal from the output of theoscillator during the intervals in which it is unquenched, and forapplying this control signal to the grid of the control tube. Anytendency for variation in magnitude of the output of thesuperregenerative oscillator will then modify the control voltageapplied to the grid of the control tube, and Will therefore modify theplate voltage both o the control tube and of the oscillator, in suchmanner as to oppose the aforesaid variation in the output signal of theoscillator.

Other objects and features of the invention following description anddrawings, in which:

Figs. l and 1A, taken together, constitute a schematic diagramillustrating one form of a system embodying the invention.

The radio ranging and tracking system shown schematically in thesefigures is described genera-ily, as to its overall operation, incopending application of William E. Bradley for Pulse Type Radio RangeTracking and Indicating System,

voltage. Upon the simultaneous occurrence of a received pulse and anunquench pulse, the cyclic control voltage, and hence the cyclicvariation in delay of unquench pulses with respect to P. R. F. pulses,is interrupted, the value of the control voltage upon interruptioncomprising a suitable indication of target range. In addition to theunquenching immediately following each P. R. F. pulse, thesuperregenerator is unquenched a number of other times before the nextP. R. F. pulse, the output of the superregenerator during unquenchpulses being used to produce automatic regeneration control (ARC) of thesuperregenerator in accordance with the present invention, as describedmore fully hereinafter.

Referring now more specifically to the schematic Figures 1 and 1A, thepulse repetition rrequency oscillator may be a cathode feedbackmultivibrator oscillator comprising triodes 96 and 91 together withtheir associated connections. This oscillator may be adapted tooscillate at a frequency of approximately 2,000 cycles per second asadjusted by the variable resistor 93. Its circuits should be designedfor maximum frevquency stability and to give a suitable rectangular waveshape. Although its frequency may vary Somewhat this will not affect theoperation of the other circuits in accordance with the invention.

The negative pulse derived from the plate of tube 91 is supplied througha differentiating circuit comprising condenser 99 and resistor H30 tothe gridof a trigger tube |36, the output of which will be a pulsecorresponding to the trailing edge of 'the negative pulse derived fromthe plate of tube 91. This pulse is fed from the plate of tube I 3 tothe grid of a trigger amplifier tube ISI and thence tol the grid of acathode follower tube |02, from the cathode load |03 of which acorresponding pulse is supplied to the grid of modulator tube |04,

which may be a type 3G45r gas tube. The cathode follower tube |92 isused to provide a low impedance drive for the gas tube modulator toavoid variations in the time of its triggering. In the output circuit ofthe modulator tube |04 is connected a resonant charging choke |95 tunedby the capacitors of delay line |06 which may have a characteristicimpedance of approximately 50 ohms and whose input iS connected to theplate of the modulator tube in the manner shown. A modulating pulsewhich may be of the order of 2,200 volts is developed across resonantchoke and is supplied, through delay line |95 for shaping purposes, tothe primary winding of pulse transformer |01. Included in thisconnection may be a transmission line |08 having a characteristicimpedance of approximately 50 ohms, since in practice magnetron |09, towhich the secondary of the pulse transformer |07 is connected, will belocated in a separate pressurized unit from the circuits heretoforedescribed. Magnetron |09 may be a type 2J39 tube operating in S bandwith a peak power output of approximate- 1y ve kilowatts.Pulsedmicrowave energy from magnetron |09 may besupplied through asection of stub-supported coaxial transmission line ||0 to a suitableradiating and receiving antenna I.

At suitable points along line H0 may be located T-R cavity |I2 andcapacity probe I|3 for signal take-olf, the exact functions ofwhich'will be explained in further detail hereinafter.

Negative pulse signalsat the pulse repetition frequency of 2,000 cyclesper second are also supplied from the plate of trigger tube |36 to theplate of tube H5, which together with tube |I6 and associatedconnections comprises a cathode feed-back, non-oscillatorymultivibrator. The function of this multivibrator is to generatepositive pulses of varying duration whose leading edges correspond tothe trailing edges of negative pulses generated by the P. R. F.oscillator. Its mode of operation is generally as follows: The grid oftube I I6 is normally biased more positive than the grid of tube |I5 soas to cause tube ||6 normally to conduct. It should be noted, however,that the bias on tube IIS is determined not only by the potentialapplied to its grid but also by the drop in the cathode resistor 48during the time the tube is conducting. Tube II5, on the other hand, isnormally cut 01T. Upon the occurrence of a negative pulse supplied to itthrough connection ||4 from the plate of tube |36, the grid of tube II6will be driven suiiiciently negative to cut off the tube. When thishappens the cathode of tube I|5 as Well as the cathode of tube ||6 willbe reduced to ground potential and tube |I5 will begin to conduct. Thecurrent drawn by tube I l5 will of course depend upon the bias appliedto its grid from potentiometer |26. As tube ||5 begins to conduct itsplate will Ygo negative and apply a negative impulse to the grid of tubeII@ to maintain it cut oif. Howeverthis effect will gradually beovercome, as condenser I3`l charges through tube H5, until a point isreached at which tube |I5 again conducts. The circuit is then incondition to repeat its cycle in response to the next pulse suppliedfrom the trigger tube. The duration 'of pulses generated by this delaymultivibrator will be variable, depending upon the grid bias on tube I5,from 1 to 14 microseconds. From these varying width delay pulses adiierentiated signal is derived across the resistor I I8 of adifferentiating circuit comprising this resistor and condenser I I l,and the negative pulses, corresponding to the trailing edges of thevariable Width pulses from the delay multivibrator, are supplied to thegrid of tube I9, which together with tube |20 andv associatedconnections comprises an amplier for this pulse. The output of thisamplifier is fed to the plate of tube |22 which, together with tube I2Iand associated connections, comprises a freely oscillating cathodefeed-back multivibrator adjusted to oscillate at a frequency somewhatbelow the A5th harmonic of the pulse repetition frequency oscillator (e.g. 9.8 kc.). The negative pulse supplied to this oscillator from thepreceding amplifier serves to synchronize it by initiating a series ofpulses at the 9.8 kc. rate, the initial pulse of this series being madeto coincide exactly with the trailing edge of the variable durationpulse generated bythe delay multivibrator. These generated pulses aredifferentiated in a network comprising condenser |40 and resistor |41and the negative pulses, resulting Vthrough voltage divider |26 fromsweep tube |24.

The latter may consist of a type 2D21 gas tube, between the plate ofwhich and ground isconnected a condenser |25. The other constants ofthis circuit are adjusted so that the sweep tube will normally developacross condenser |25 a sawtooth voltage having a recurrence frequency ofapproximately 10 cycles per second. This voltpulse to increase further,and the system to -age causes the potential on the gridof tube` of thedelay multivibrator to vary, thereby varying the duration of the pulsesgenerated bythe :delay multivibrator from 1 toli microseconds"l0 timesper second. There may also be provided between the plate of tube |24 andground,- a

switch |21 which, when closed will discharge the "condenser |25 at anyarbitrary time and rein'iti- `ate the sweep. This switch is referred toasan iii-switch and its purpose is to permit the-life- `initiation ofthe sweepvat any desired time lin tomlfl microseconds, corresponding toranges of from 165 to 2300 yards. However a sweep cut-:off

tube |29, which may also be a type 2D21ggas tube, is connected in shuntwith condenser |25 and is supplied through connection |28 with pulsesfrom the superregenerative receiver output, corresponding to received,target-reflected signals, to discharge the condenser |25 by apredetermined amount determined by resistor V|38 whenever such a pulseis received. The amount by which the condenser |25 is discharged by Sucha pulse is made such that the voltage to which the grid of tube ||5 ofthe delay multivibrator 'is reduced corresponds to a delay somewhat lessthan the time actually required for the preceding Vreflected signal tobe received from the target. '.This is to take account of any diminutionof the distance from the equipment to the target. There may also beprovided an out-switch |30, connected between the grid of tube |29 andground,

which, when momentarily closed, will prevent a given received signalfrom actuating the sweep cut-01T tube, thereby permitting the sweepvoltage to continue rising, the width of the ldelay search for andultimately lock on a more distant target. A range signal proportional tothe peak voltage across condenser |25 may be derived directly fromdivider |26 and supplied through conne'ction |3|, and an integratingcircuit comprising resistor |32 and condenser |33, ,tor-the grid of tube|34. The output from this tube, derived across a cathode load impedance|39, may be supplied to a suitable range indicator |35.

There will now be explained in detail the operation of thesuperregenerative receiver, and its associated circuits. Received,target-reflected 'signals derived from T-R box ||2 are mixed with asignal from local oscillator |11 in crystal mixer |18 and the resultingintermediate frequency is supplied therefrom through transmission line.;19 to the inputof buffer preamplifier tube |80. .alt is to be noted thatthe primary function of this tube is to prevent radiation through theantenna of signal from the superregenerator and that, except for thisrequirement in certain military applications, the tube might be omittedinasmuch as sumcient amplification is provided by the superregeneratoralone. In order accurately to maintain the frequency of the localoscillator |11,

which may comprise a type 2K28 klystron, an automatic frequency controlcircuit is employed.

. To this end, received signals derived from another point ontransmission line I0 by means of capacity probe I3 are mixed in crystalmixer 2 96 with local oscillator signal supplied through connection 298.The resulting signal is amplied in a suitable intermediate frequencyamplifier 291 and supplied to a conventional discriminatorcomprisrunstubes :sa and `299 and associated.. circuits Y From the output of thediscriminator are deriv'd positive or negative pulses, the polarity ofwhich will depend upon the relation between the transmitter and localoscillator frequencies as compared to the intermediate frequency tuningof the discriminator. These pulses are amplified in the pulse amplifiertube 300 and are supplied from the output thereof to the grid of a gasdischarge tube 30|. The latter is connected in shunt with a second gasdischarge tube 302 which; together with condenser 303, constitutes asawtooth oscillator which may be adjusted to operate at a low frequencyof.n for example, 5 cycles per second. The voltage developed acrosscondenser 303 is supplied through connection 304 to the repeller oflocal oscillator tube |11 to vary its frequency through a rangecomprising those frequencies which, when mixed with frequencies withinthe range at which the transmitter might operate, will yield the desiredintermediate frequency. Thus the gas tube oscillator will tend to sweepthe frequency of the local oscillator |11 through this range 5 times persecond. However the positive pulses from the pulse amplifier 300,appearing on the grid of tube 30|, will cause it to conduct whenever thefrequency of the transmitter exceeds the frequency to which thediscriminator is tuned. This will discharge condenser 303 by a certainamount so as to tend to maintain the voltage thereacross.- and hence thefrequency of local oscillator |11, constant.

The left hand triode section of tube |8|, together with tank circuit|82, comprise a superregenerative oscillator which may be adjusted tooperate at a frequency in the neighborhood of 60 megacycles. Pulses ofintermediate Vfrequency energy corresponding to target signals will besupplied to tank circuit |82 through connection |83 and an inductor |84coupled to the tank circuit inductance. Unquenching pulses at the quenchoscillator rate of 10 kilocycles, and variably delayed with respect totransmitted pulses from the P. R. F. oscillator, will also be suppliedthrough connection |23 to a damping circuit comprising double diode |86and inductor |85 coupled to the inductor of tank circuit |82. Asheretofore explained these unquenching pulses have been steepened andnarrowed to a width of approximately one-half microsecond by means "fthe differentiating network |40, |4|. Since the unquenching pulses occurat a higher frequency than the received target pulses, received signalswill not be present in the tank circuit |82 upon the occurrence of everyunquench pulse. In the presence of received signals oscillations in thetank circuit |82 will build up more rapidly,` and to a higher levelduring the unquench interval. than in their absence. This differencebetween absence and presence of signal is shown at |81 and |88respectively. The rate of build-up of oscillations may be adjusted sothat, in the absence of received signal, they will not build up duringthe unquench interval beyond the level S, while, ln the presence ofreceived signal, they will build up appreciably beyond level S. Thisadjustment is conveniently made by adjustment of the coupling betweeninductors |84 and |82 and by adjustment of the tuning of the circuitcomprising inductor |84 and condenser 54 to differ somewhat from theresonant frequency of tank circuit |82. It will be apparent also thatthe duration of the unquench interval is an important factor incontrolling the difference between the output of the superregenerator inthe presence and in the absence of received signal. As already mentioned.`-.theduration of thisl intervalicanreadilyhe con'- trcllecl bydifferentiating or otherwise 4narrowing the pulses generated bythequench. oscillator -multivibraton 'I'o distinguish between the output of.the superregenerator with and .withoutfre- .ceivcd signalsgthere wasutilized, in thisembodi- ,ment of the invention, a cycle countercomprising condenser |89, a Apair of diodes. |90, resistor |9| andcondenser |92. One of the diodes has its plate connected toone'side ofcondenser |89 and its cathode connectedA to ground through a load l-impedance. comprising resistor |9| and ,condenser .192; a The otherhasits' cathode connected to the esame sideof condenser |89 and its platecoriinected, to ground. Condenser |89 may :have a relatively smallcapacitance of the order of .n'ncromicrofarads, while condenser |92 maybe of theorcler of 100 micromicrofarads and resistor :19t of the orderof 100,000 ohms. On eachpositive cycle of. thev superregenerative'oscillator which exceeds the predetermined amplitude level f8 the twocondensers will be charged through the {right-hand diode, While'on thenegative cycle the other diode will discharge condenserV |09 withoutalecting the charge on condenser |92, thus -voltage will be developedacross condenser |92, -the ultimate magnitude of which will bedetermined by the number and amplitude of the cycles of thesuperregenerative oscillator during the interval of unquenching. Clearlythe magnitude vof this voltage will be greater in the presence of 'areceived signal. than in its absence. This voltage vis amplified. in apulse amplifier comprising tubes `maand |94 and the output is suppliedthrough connection |28 'to the grid of sweep cut-oir tube.

ing the superregenerative oscillator at a` substan-` -tially higher:frequency than the P. R. ire ^.1que'ncy,'it ispossibleto utilize itsno-senal output tov operate an` automaticregenerationncontrol circuitfor maintaining the desired sensitiv- .ity loi the superregenerativereceiver. 'Ifo Atlfiis rend, output from ,the pulse amplifierinteffgrated by .a peak detector comprising diode |95, resistor |95 andcondenser le?. This peak detector may have a time constant of the orderof 'w40 micro-seconds, which is approximately two- "fths vof theinterval between pulses of the 4quench oscillator. A'time constant oithis order -of magnitude.- which is long lay-comparisonA with 'therecurrence period ci pulses from the quench Voscillator and'shortcomparedv .to .the intervals .between received pulses, vpermits-the peakldetector-output to return to its level in the-absence fof receivedsignal. following each received signal "and prior. to the .occurrence ofanother. Thus there is no A. V. C. action andthe output of the peakdetector is'not such'as to impairthe` sensitivityof the superregeneratorwhich it is'to control; This output, afterlitering, is applied `throughconnection |98 to the lgridoi the other triode section of tube i9 l',whose plateis connectie'd to the plate of the irst section, and thusconftrols the rate'of buildup of oscillations in the suprregene'rator. A

` Subject matter shown and' ldescribed in' this specification but notclaimed herein is claimed" Simultaneous occurrence during a ltimeinterval.

"in @pending applications assigned te the-assignee ofthe presentinvention as follows:

The following subject matter, in copending application of William E.Bradley, Serial Number 651,398, led March 1, 1946:

(l) A radio ranging system employing a transmitter ofv time-spaced pulsesignals, a producer of other time-spaced pulse signals normally delayed.by varying time intervals with reference to sai-d transmitter pulses, areceiver of object1'enected transmitted pulses.. and means responsive tothe 4simultaneous occurrence of received and. producedpulses forsubstantially altering the delay `of produced pulses with referencetotransmitted pulses. .v l The following subjectV matter in copending'ap- 'plicationof Wilson P. Boothroyd and Albert L. gFree, Serial Number651,888, Vfiled March 4, 1946:

.produced pulses Vwith reference to transmitted pulses in a manner telprevent another such-'sipredetermined v(2) The representative embodimentof such ja E:system employing a sweep circuit, comprising Ea gas tubeand a condenser, and a separate gas tube for discharging the condenserby a predetermined amount upon the simultaneous'occurvrence ofreceived'and-produced pulses, as shown and described with reference toFigures l and 1A of this specification.

l(il) In a system of this sort, the method of 'and means fordifferentiating or otherwise narrowing and/or steepening quench pulsesYin order v-to achieve an appreciable differencebetween-superregenerative receiver output in the presence and in theabsence of received signal, as shown-and described with reference toFigures 1 and 1A of as to cause the system to seek targets at eithercloser- 4orgreater' range as shownlandy described with reference toFigurev l. I y The following subject matter in c'opending application ofJoseph C. Tellier,l Serial Number 658,894, filed April V2, 1946:

(l) The cycle-'counting arrangement, comprising a pair of diodesiorindicating the difference in output of a superregenerative receiver iinthe presence land in the absence of received signal, as showin anddescribed with-referenceto -Figures 1 'and 1A of this-specification.

AThe following subject matter in 'copendi'ng application of William` E.Bradley, Serial NumberV 660,037, led April 6, 1946:

1) The quenching circuit for a .superregenerative receiver, comprising apair of diodesop- -postely connected and coupled to. the tank circuit ofa superre'generative receiver, as shown fand described with reference toFigure 1A of this specification.

I claim:

an' oscillator, said vacuum tube having at least 'triode elements,aportion of said-resonant tank circuit bei-ngi connected betweenthegridand cathode of said vacuum tune and a portion of said tank circuit beingincluded in the anodecathode circuit of said vacuum tube, means forsupplying input signal to said oscillator, means for deriving outputsignal from said oscillator, means for effecting alternate quenching andunquenching of said oscillator, a, second vacuum tube having at leasttriode elements, said lastnamed vacuum tube having its anode and cathoderespectively connected to the anode and cathode of said rst-named vacuumtube, means responsive to the output from said oscillator for developinga control signal, and means for applying said control signal to thecontrol grid of said last-named vacuum tube to control the rate ofbuild-up of oscillations in said oscillator and thereby to control thesensitivity of said superregenerative receiver.

KENNETH H. EMERSON.

REFERENCES CITED The following references are of record in the le ofthis patent:

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